Automatic fastener machines can drill, countersink, insert and squeeze a rivet in a workpiece in approximately 3.5 seconds when average materials are being joined. Such machines generally automatically gauge the depth of the countersink and determine the height, or upset, of the formed head. The height of the upset is determined from the bottom of the workpiece. Head formation and workpiece support is accomplished by the lower anvil assembly of the fastener machine. The determination of head height and proper workpiece support requires that the lower anvil assembly be positioned directly below the upper ram of the fastener machine because the upper ram performs the functions of drilling, countersinking and inserting the rivet into a hole.
Because the lower anvil body must be closely positioned to the upper ram the anvil can be easily damaged either by a drill during the drilling function or because of some misalignment or because a rivet may be harder than specification. In the past when the lower anvil was damaged, several hours were required to disassemble the fastener machine, replace the damaged anvil and reassemble and align the machine so that work could be resumed. Not only was the repair procedure time consuming, resulting in loss of substantial amounts of production time, it was also expensive because replacement anvils are costly, and for the most part, almost impossible to repair.